Termination of sustained atrial flutter and fibrillation using low-voltage multiple-shock therapy

Abstract

Background: Defibrillation therapy for atrial fibrillation (AF) and flutter (AFl) is limited by pain induced by high-energy shocks. Thus, lowering the defibrillation energy for AFl/AF is desirable.

Objective: In this study we applied low-voltage multiple-shock defibrillation therapy in a rabbit model of atrial tachyarrhythmias comparing its efficacy to single shocks and antitachycardia pacing (ATP).

Methods: Optical mapping was performed in Langendorff-perfused rabbit hearts (n = 18). Acetylcholine (7 ± 5 to 17 ± 16 μM) was administered to promote sustained AFl and AF, respectively. Single and multiple monophasic shocks were applied within 1 or 2 cycle lengths (CLs) of the arrhythmia.

Results: We observed AFl (CL = 83 ± 15 ms, n = 17) and AF (CL = 50 ± 8 ms, n = 11). ATP had a success rate of 66.7% in the case of AFl, but no success with AF (n = 9). Low-voltage multiple shocks had 100% success for both arrhythmias. Multiple low-voltage shocks terminated AFl at 0.86 ± 0.73 V/cm (within 1 CL) and 0.28 ± 0.13 V/cm (within 2 CLs), as compared with single shocks at 2.12 ± 1.31 V/cm (P < .001) and AF at 3.46 ± 3 V/cm (within 1 CL), as compared with single shocks at 6.83 ± 3.12 V/cm (P =.06). No ventricular arrhythmias were induced. Optical mapping revealed that termination of AFl was achieved by a properly timed, local shock-induced wave that collides with the arrhythmia wavefront, whereas AF required the majority of atrial tissue to be excited and reset for termination.

Conclusion: Low-voltage multiple-shock therapy terminates AFl and AF with different mechanisms and thresholds based on spatiotemporal characteristics of the arrhythmias.

Figure 1. Experimental Setup

(a) Photograph of a typical preparation with shock meshes labeled, located 10 cm apart. The black circles represent the locations of pacing/sensing electrodes. (b,c) Typical activation map and optical action potentials (OAPs) during pacing of the RAA (300 ms). (The deep blue areas in the center represent pixels that have been excluded from analysis due to noise from sutures and connective tissue.) (d) Average ERP before and after ACh. (e) Representative OAPs from the RAA before and after the addition of 5 μM ACh reflecting a 57% decrease in the action potential duration.

Figure 2. Typical Atrial Flutter and Fibrillation

(a,b) Typical activation maps, representative of one arrhythmia cycle, and OAPs (as indicated by the black squares) of AFl and AF, respectively. Dashed black lines with arrows show the location and direction of the reentrant circuits. (c,d) Frequency distribution for typical examples of AFl and AF, respectively.

Figure 3. Application of ATP to AFl

(a) Representative electrograms of termination, failed termination, and conversion to AF upon application of ATP (8 pulses, 50–100% of arrhythmia CL) to AFl from the RAA and lower RA. (b) Distribution of outcome during application of ATP to AFl. (c) Percentage of therapy success as a function of CL.

Figure 4. Far Field Excitation

(a,b) Activation maps resulting from opposite polarity shocks at a field strength of ±0.05 V/cm. The dotted black line demarcates the AV groove. (c) Average shock field strength of both polarities (0.097±0.06 V/cm). (d) Activation of the ventricles at a physiological AV delay (76 ms) due to far field excitation of the atria with a shock field strength of 0.05 V/cm. (e) Simultaneous activation of the atria and ventricles with a higher voltage shock (5 V/cm).

Figure 5. Defibrillation Thresholds

(a) Defibrillation thresholds for single shocks, multiple shocks delivered within 1 CL, and multiple shocks delivered within 2 CL. (b,c) Defibrillation thresholds for single shocks and multiple shocks (3–5) delivered within 1 arrhythmia CL for AFl and AF, respectively.

Figure 6

Defibrillation Threshold as a Function of Arrhythmia CL.

Figure 7. Application of Multiple Shocks to AFl

(a) In this example of successful arrhythmia termination, four 10 ms shocks (0.3 V/cm) were applied during one CL of AFl (70 ms). OAPs are shown from the RAA and LAA before and after termination. (b) Activation maps reconstructed from the dV/dt_max of the OAPs denoted by 1–3 in panel (a). (c) In this example of unsuccessful arrhythmia termination, five 10 ms shocks (0.25 V/cm) were applied during one CL of the same arrhythmia. (d) Activation maps reconstructed from the OAPs denoted 1–3 in panel (c). The asterisks in panels (b,d) represent the shocks indicated in panels (a,c).

Figure 8. Application of Multiple Shocks to AF

(a) In this example of successful arrhythmia termination, four 10 ms shocks (10 V/cm) were applied during one CL of AF (55 ms). OAPs are shown from the RAA and LAA before and after termination by the shocks shown. Arrhythmia wavefronts, reconstructed from the dV/dt_max, before, during, and after shock application. (b) In this example of unsuccessful termination, three 10 ms shocks (2 V/cm) were applied during one CL (50 ms). Arrhythmia wavefronts before, during, and after shock application. Arrhythmia wavefront frames indicated by red lettering indicate those reconstructed during shock application.